The present invention relates to a drive control technology for a brushless motor, and a technology effective if applied to start-up control of a three-phase DC motor and sine wave current control, e.g., a technology effective when used in a drive control device of a spindle motor, which rotatably drives a disk type storage medium like a hard disk (hard disk drive) system.
A brushless three-phase DC motor generally called a spindle motor is used to rotate a magnetic disk in a hard disk drive. The magnetic disk is rotated at high speed by the spindle motor. A read/write magnetic head is made close to the surface of the rotated magnetic disk, and information is written therein and read therefrom while the magnetic head is being moved in a radial direction of the disk.
There has heretofore been known a system in which in drive control of a brushless motor, the relationship of position between a rotor and a stator is detected using a Hall element and a coil phase to start its energization is determined from the detected positional relationship to thereby prevent the motor from being reversely rotated. However, since it becomes difficult to scale down or downsize the motor when a rotor position detector using the Hall element is attached to the motor, a sensorless motor is moving toward heavy use in the hard disk drive. In such a sensorless motor, the rotor might be reversely rotated upon starting of its rotation if the relationship of position between the rotor and stator is not recognized.
Therefore, a control system has been proposed by the present applicant, wherein such short pulse currents that a rotor does not responds, are respectively caused to flow through any two of three phase coils, and the polarity of an induced voltage appearing at each de-energized phase is detected, thereby determining the relationship of position between the rotor and a stator, and each phase to start energization is determined using characteristics in which the polarity of each induced voltage is switched every 180° as electrical degrees, whereby reverse rotation of a sensorless motor at its start-up is avoided (see Patent Document 1).
On the other hand, the hard disk drive needs a reduction in vibration of the spindle motor in order to achieve high recording densification, and a reduction in noise of the spindle motor in order to improve a work environment. Sine wave current driving is effective for the reductions in vibration and noise. To this end, the invention has been proposed wherein sine wave-shaped currents are caused to flow through coils for respective phases to thereby smoothly rotate a rotor.
Even when a drive current is caused to flow in phase with a back electromotive voltage developed in each coil, the multi-phase DC motor obtains the maximum torque. Thus, a system for detecting a back electromotive voltage developed in each coil and performing rotational drive control has generally been adopted.
However, the system for detecting the back electromotive voltage of the coil to perform the rotation drive control needs to provide a de-energized period in which no current is caused to flow through each coil, to detect the back electromotive voltage, thereby causing vibrations in rotation and leading to the occurrence of noise and vibrations. There has therefore been proposed a system wherein a current flowing through a coil is detected without detection of a back electromotive voltage to thereby form a drive waveform (see Patent Document 2).
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2001-275387
[Patent Document 2]
Japanese Unexamined Patent Publication No. 2001-314090